SSA simplify passs

[Henry Cejtin]

The  VM  in  Linux  definitely  had problems even as recently as 2.4.16, with
2.4.17 being the first one that seems ok.  The earlier versions would go in a
mode  where  they  would not use memory for programs that was currently being
used as a file system cache.  This was really a big  problem   on  big-memory
machines.  It made things pretty hopeless for Rico on his machines with 4 gig
of RAM, where he would not be able to get above 1 gig total for programs.